The regulation of gene expression is a fundamental process in cells, and alterations in this process have been linked to numerous disease states in humans. It is regulated at multiple levels, and determining how these events are coordinated is central to understanding gene expression. The yeast Ccr4-Not complex was originally described as a regulator of the general transcription factor TFIID. Remarkably, it has now been implicated in multiple aspects of gene regulation including mRNA degradation, translational silencing, histone methylation and protein ubiquitylation. Its myriad of functions is quite fascinating and suggests it regulates gene expression from the birth to death of a gene product. Our study of TFIID and DNA damage inducible genes led us to characterize this complex, as it appears to play a role in regulating DNA damage stress responses. Over the last funding period we established it as a bona-fide elongation factor that directly activates arrested RNA polymerase II (RNAPII). Interestingly, Ccr4-Not appears to function via a mechanism unique from other elongation factors characterized to date; thus, analyzing its function has the potential to reveal novel insights into how factors regulate RNAPII. We have a developed a number of powerful assays to fully exploit the biochemistry, powerful genetics and genomics of yeast to characterize its mechanism of action and the role it plays in gene expression in vivo. The goals of the studies described in this proposal are to investigate the structure of arrested elongation complexes bound by Ccr4-Not to gain a greater understanding of how it promotes elongation; to explore its collaboration with other elongation factors to regulate RNAPII activity; to analyze the physiological functions of the complex in vivo by mapping changes in RNAPII arrest across the genome in Ccr4-Not mutants. The long term goals of this project are to understand how this multi-functional complex regulates multiple steps in gene regulation to maintain normal development and the integrity of the genome in eukaryotic cells.